The complaints system for financial services is not working, judging by the extraordinary gulf between good and bad practice laid bare in figures from the Financial Ombudsman Service today.

Nine out of 10 of the complaints involving payment protection insurance against Lloyds in its various forms (including Bank of Scotland and Halifax) are found in favour of the customer. In contrast nine out of 10 of the complaints against Nationwide Building Society are found against the customer.

Yet Lloyds and Nationwide should be working to identical guidance from the Financial Conduct Authority. They have also both received the same guidance from the ombudsman about how to deal with PPI complaints. They both have the same regulatory duty to follow the "treating customers fairly" rules.

Are some banks using the ombudsman as their dumping ground for complaints? Is there a cynical calculation that leads some banks to bounce off complaints, on the presumption that many, if not most, people cannot be bothered to take their case further?

In June, evidence emerged that at a Deloitte-run call centre, staff were encouraged to delay and deny compensation requests involving Lloyds in the hope they would be dropped.

The ombudsman appears to have reached the same conclusion, although the language is couched more delicately. "Disappointingly we are still seeing cases where businesses are not following our long-standing approach to PPI," said chief ombudsman Natalie Ceeney.

The ombudsman service was never intended to be the first port of call for complaints. It is only after a complaint has been seriously investigated, and where the two parties have reached deadlock, that the case should escalate.

While Lloyds boss Antonio Horta-Osorio was at Santander, it became a byword for poor service and high complaint levels. The ombudsman figures show Santander is now improving fast, with the total number of complaints down on the six months before. At Lloyds it is going in the other direction. It had 129,293 complaints, up 38%, and compares dreadfully to HSBC, with 18,444 complaints, and Santander, with less than 10,000.

Lloyds has become the outlier on complaints, even taking into account its size. Horta-Osorio needs to act fast – or the regulators should take tougher action to bring it into line.